"Chen, Tim C" <tim.c.c...@intel.com> writes:

>>
>>So this is impossible without THP swapin. While 2M swapout makes a lot of
>>sense, I doubt 2M swapin is really useful. What kind of application is 
>>'optimized'
>>to do sequential memory access?

Anything that touches regions larger than 4K and we want to do the
kernel do minimal work to manage the swapping.

>
> We waste a lot of cpu cycles to re-compact 4K pages back to a large page
> under THP.  Swapping it back in as a single large page can avoid
> fragmentation and this overhead.

Also splitting something just to merge it again is wasteful.

A lot of big improvements in the block and VM and network layers
over the years came from avoiding that kind of wasteful work.

-Andi

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